The present invention relates to pressure-responsive relief valves for limiting fluid pressure. In fluid lines, diaphragm-type regulators are commonly used to reduce and/or control the line fluid pressure. Many of these have a pilot line from a distance downstream for applying fluid pressure to the diaphragm. To protect the diaphragm from excessive pressure, a relief valve or other protective device is sometimes placed in the pilot line.
Also, in the case of valuable instruments and other controls, a protective device is sometimes placed in the fluid line to the instrument or control.
The practice in the past has been to place a pressure-responsive "pop-off" valve which merely vents the control line, without regard to maintaining sufficient pressure on the regulator to keep it closed.